The present application relates to the field of x-ray and computed tomography (CT). It finds particular application with CT security scanners. It also relates to medical, security, and other applications where identifying sub-objects of a compound object would be useful.
Security at airports and in other travel related areas is an important issue given today's sociopolitical climate, as well as other considerations. One technique used to promote travel safety is baggage inspection. Often, an imaging apparatus is utilized to facilitate baggage screening. For example, a CT device may be used to provide security personnel with two and/or three dimensional views of objects. After viewing images provided by the imaging apparatus, security personnel may make a decision as to whether the baggage is safe to pass through the security check-point or if further (hands-on) inspection is warranted.
Current screening techniques and systems can utilize automated object recognition in images from an imaging apparatus, for example, when screening for potential threat objects inside luggage. These systems can extract an object from an image, and compute properties of these extracted objects. Properties of scanned objects can be used for discriminating an object by comparing the object's properties (e.g., density, shape, atomic characteristics, etc.) with known properties of threat items, non-threat items, or both classes of items. It can be appreciated that an ability to discriminate potential threats may be reduced or degraded if an extracted object comprises multiple distinct physical objects. Such an extracted object is referred to as a compound object.
A compound object can be made up of two or more distinct items, at times referred to herein as sub-objects. For example, if two items are lying side by side and/or touching each other, a security scanner system may extract the two items as one single compound object. Because the compound object actually comprises two separate objects, however, properties of the compound object may not be able to be effectively compared with those of known threat and/or non-threat items. As such, for example, luggage containing a compound object may unnecessarily be flagged for additional (hands-on) inspection because the properties of the compound object resemble properties of a known threat object. This can, among other things, reduce the throughput at a security checkpoint. Alternatively, a compound object that should be inspected further may not be so identified because properties of a potential threat object in the compound object are “contaminated” or combined with properties of one or more other (non-threat) objects in the compound object, and these “contaminated” properties (of the compound object) might more closely resemble those of a non-threat object than those of a threat object, or vice versa.
Numerous techniques have been developed to separate a compound object into its sub-parts and improve threat item detection, and thereby increase the throughput and effectiveness at a security check-point. One of the more common techniques is compound object splitting. Compound object splitting essentially identifies potential compound objects and splits them into sub-objects using a histogram-based compound object splitting algorithm. Other techniques include using surface volume erosion to split objects. However, using erosion as a stand-alone technique to split compound objects can lead to undesirable effects. For example, erosion can reduce a mass of an object, and indiscriminately split objects that are not compound, and/or fail to split some compound objects. Additionally, in these techniques, erosion and/or splitting may be applied universally, without regard to whether an object is a potential compound object at all.